Somatomedin, a growth hormone dependent plasma factor(s) mediating the tissue response to somatomedin, exists in at least two forms. "Big SM" with a molecular weight of at least 60,000 is the form found in whole plasma under neutral or slightly basic conditions. "Small SM" with a MW of about 5-12,000 daltons is the form found after acid ethanol extraction, and is the form upon which most purification work has been done. The goals of this project are to: 1) Clarify the relationships between Big SM and Small SM; 2) Compare the in vitro and in vivo actions of Big SM and Small SM; 3) Explore whether intracellular cGMP can be used as an assay of positive pleiotypic effect. BIBLIOGRAPHIC REFERENCES: Hintz, Raymond L. Somatomedin. Trace Components of Plasma: Isolation and Clinical Significance (Eds. G.A, Jamieson & T.J. Greenwalt) Alan R. Liss, Inc. New York. 1976, pp. 217-223.